This application claims the priority of Japanese Patent Application No. 2001-354909 filed on Nov. 20, 2001, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary optical filter apparatus arranged within an optical path in an illumination optical system of a projection type image display apparatus or the like, for example, in order to change the color of illumination light periodically; and, more specifically, to a rotary optical filter apparatus integrated with a cooling fan, comprising a fan for cooling an optical filter, and an illumination optical system using the same.
2. Description of the Prior Art
Color wheel apparatus employed as color separating means have been known in illumination optical systems of projection type image display apparatus for optically modulating illumination light by image display devices such as liquid crystal display and digital micromirror device (hereinafter referred to as xe2x80x9cDMDxe2x80x9d) and projecting thus modulated light under magnification. A color wheel apparatus comprises a disk-shaped optical filter rotated at a high speed by the driving force of an electric motor or the like, whereas the optical filter is divided into a plurality of regions along its circumferential direction. Further, each of thus divided regions is processed so as to exhibit a predetermined optical characteristic, for example, by vapor deposition of a multilayer film such as dichroic film.
While rotating, the optical filter is continuously irradiated with a light beam outputted from a light source, thereby being heated considerably.
Recently, projection type image display apparatus have been desired to project images with higher luminance and make the apparatus smaller, whereby the output of the light source light has been made greater while the color wheel apparatus have been made smaller. As the color wheel apparatus have been made smaller, the diameter of the luminous flux from the light source for irradiating the optical filter has been made further smaller, whereby the amount of irradiation per unit area of the optical filter has increased. As the output of the light source light has further increased, the extent to which the optical filter is heated has increased remarkably.
As a consequence, the moisture existing in the multilayer film deposited on the optical filter may be released, for example, thus yielding the possibility of the optical filter failing to keep a predetermined optical characteristic. For keeping a predetermined optical characteristic, an optical filter excellent in heat resistance may be used. However, such an optical filter is so expensive that the manufacturing cost may increase when it is used.
For preventing optical characteristics of an inexpensive filter from deteriorating, a fan for cooling the optical filter may be provided so as to suppress the heating. However, newly providing a fan for cooling the optical filter necessitates not only the fan but also an electric motor for driving the fan, whereby a space for installing them and the resulting increase in mass may become problematic.
Japanese Unexamined Patent Publication No. 2001-100315 discloses an apparatus in which a filter face of a color wheel apparatus is provided with blades, so that cooling winds are generated as the color wheel rotates. It is advantageous in that no driving motor for the fan is necessary since the color apparatus itself acts as a cooling fan. However, this color wheel apparatus is configured just for cooling a video display device. Providing only the blades having the configuration as disclosed is hardly effective in cooling the color wheel itself, and is hard to guide cooling winds to other places.
In view of the foregoing circumstances, it is an object of the present invention to provide a rotary optical filter apparatus integrated with a cooling fan, equipped with a fan function for effectively cooling an optical filter, preventing the optical filter from overheating, and making inexpensive filters usable without deteriorating their optical characteristics; and an illumination optical system using the same.
For overcoming the problems mentioned above, the present invention provides a rotary optical filter apparatus integrated with a cooling fan, comprising a rotary holder axially supported with respect to a predetermined rotary axis; and an optical filter having a filter face formed so as to exhibit a predetermined optical characteristic, the optical filter being rotated together with the rotary holder while being held by the rotary holder such that the filter face is substantially orthogonal to the rotary axis; wherein the cooling fan is a sirocco type cooling fan comprising a plurality of fan blades, each having a wing-shaped cross section extending radially of the rotary axis, arranged circumferentially of the rotary axis at respective positions outwardly separated from the rotary axis, the cooling fan being supported by the rotary holder so as to be integrally rotatable with the optical filter, the cooling fan inhaling an air from a center part and discharging thus inhaled air from an outer peripheral part due to an action of the fan blades upon rotating, so as to make an airflow along the filter face and cool the optical filter.
The fan blades may be forwardly inclined by a predetermined angle in the rotating direction. This enhances the effect of directing the airflow to the filter face.
The rotary optical filter apparatus may further comprise a fan cover having a housing for covering the rotary holder, optical filter, and cooling fan, the housing being formed with an intake port for taking an air therein from outside and an exhaust port for blowing the air discharged by the cooling fan into a predetermined direction in a centralized manner.
When the optical filter is a transmission type optical filter, the housing may be formed with an entrance opening for making a luminous flux from a light source section incident on the optical filter within the housing and an exit opening for discharging from the housing the luminous flux transmitted through the optical filter, each of the entrance and exit openings having a light-transmitting sheet attached thereto.
The optical filter may be an optical filter decomposing a white luminous flux from a light source section into three colors of R, G, and B in a time-division manner and outputting thus decomposed color light components.
The present invention provides an illumination optical system for outputting light from a light source section as predetermined illumination light, the illumination optical system comprising the rotary optical filter apparatus integrated with a cooling fan in accordance with the present invention.
The illumination optical system may comprise the rotary optical filter apparatus integrated with a cooling fan in accordance with the present invention in which the optical filter is an optical filter decomposing a white luminous flux from a light source section into three colors of R, G, and B in a time-division manner and outputting thus decomposed color light components, and a digital micromirror device irradiated with the luminous flux outputted by the optical filter as being decomposed into the three colors in the time-division manner.